The main objective of the proposal namely individualized monitoring and modulation and its role on a better modality of immunosuppression will be evaluated in depth. Towards this goal, three randomized groups of patient populations, each consisting of about 70 patients will be analyzed. Group I will consist of 5 fixed doses of ATG. Group II will consist of 5 fixed doses of ATG plus the administration of ATG based on immunomonitoring. Group III will be comprised of 5 fixed doses of ATG plus the administration of an average dose of ATG given to Group II. This group was added on, in order to define the role of quantity of ATG administered vs. immuno-monitoring. Monitorng of immune reactivity in early post-transplant period will comprise of (1) total circulating T-cell levels; (2) PHA and con-A blastogenesis as measured twice weekly for the first month, then weekly until discharged. (3) LDA to be assayed on weakly serum samples. Since this test does not affect the modulation, we plan to perform it on a retrospective basis using multiple samples. (4) MLC and CML are to be measured during the 3rd and 5th week after transplant, then at 3 month intervals.